合成噴流衝擊於平板之熱傳研究

Abstract

現今的儀器舉凡電腦等由於效能愈來愈好，因此所產生的熱量也相對增大，而當電子產品內部電子元件一旦有廢熱無法有效排出，則溫度會逐漸升高，電子產品將會無法正常運作，儀器將容易當機而降低使用壽命。故如何降低熱量則成為現今發展之問題，其中合成噴流(Synthetic jet)即為一種解決方法，我們將研究此方法來冷卻電子設備和其它設備。 本實驗使用壓電蜂鳴片做為進氣動力源，使工作流體流動衝擊於高溫表面上，並藉由改變進氣高度-直徑比(Z/d)為2至25之間、而噴嘴孔口直徑為3mm、觀測銅片面積為50×50 mm2、雷諾數為500至1300之間、壓電振動頻率為200Hz至800Hz之間，並在這些參數下，研究各種情況下衝擊冷卻的熱傳增益之影響。 由實驗結果可知，跟自然對流的熱傳係數相比，本實驗所用之合成噴流最大熱傳導係數可高達7倍以上，而平均紐森數方面，除了發現跟雷諾數成正比關係外，也發現在不同衝擊高度比且相同雷諾數時，激發頻率高的散熱效果比激發頻率低的好。

Impingement heat transfer from synthetic air jet on a heated surface is experimentally studied. Synthetic jet offers high heat transfer coefficient in compact design, which is suitable for the thermal management of electronic devices such as high-power electronic chips. The synthetic jet is produced by the high frequency oscillating motion (200 - 800 Hz) of a piezoelectric actuator. The jet Reynolds number ranges from 500 to 1,300 and the velocity profile of this synthetic jet issuing from the jet hole is measured by the hot-wire anemometer. The diameter of the jet hole is 3 mm and the jet-to-surface spacing (Z/d) ranges from 2 -25. The copper plate is square and measure 50 × 50 mm2.In this study, the effect of excitation frequency, jet-to-surface spacing, and jet Reynolds number are tested. Results showed that heat transfer enhancement with the synthetic jet are at least 7 times higher than the natural convective heat transfer. Synthetic jets were found to remove more heat when operating at high frequency and same Reynolds number.